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Plant water regime
• Introduction
• Adaptation, acclimation
• Poikilohydric and homoiohydric plants
• Water content, relative water content
• Water potential and its components
• Water and growth
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Basic characteristics
• Water content • WC [%] = (FM - DM / FM) 100• FM - fresh mass, DM - dry mass• cytoplasm 85 - 90 %, chloroplasts, mitochondria about 50 %, • ripe fruits 85 - 95 %, leaves 80 - 90 %, roots 70 - 95 %, wood 50 %,
seeds , pollen grains 5 - 15 %
• Relative water content • RWC [%] = [ 1 - (FMs - FMa)/(FMs - DM) ] 100, • FMs - mass after saturation, FMa - actual fresh mass
• Plant water balance = absorption - transpiration• Effects of soil moisture and relative humidity
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Water potential and its components
w = (w -w0) / Vw
w - water potential, w - chemical potential of water in the system, w
0 - chemical potential of pure water, Vw-- volume per mole of water
= (G / ni)T,p,nj
• G - Gibbs free energy, ni - number of moles of component i, nj - number of moles of other components, T - absolute temperature, p - pressure
w = s + p + m + g
s - osmotic potential, p - pressure potential, m - matric potential, g - gravitational potential
s = (RT / Vw) ln aw = -cRT• R - gas constant, aw - water activity, c - concentration
= V (p / V) - volumetric modulus of elasticity , V - cell volume
• Differences in w and its components inside cells and in apoplast (wall a tissue)
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Methods of determinationw - psychrometric methods, pressure bomb s - psychrometric and cryoscopic methodsp - pressure probe
Thermocouple psychrometer
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Pressure chamber
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Pressure probe
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uplatnění
Hofler diagram
• The roles of individual components:
g - high trees
m - imbibition and germination (till water content about 60 %)
p - veins, apoplast, growth, movements of stomata
s - transport on cell and tissue level, plasmolysis, plasmoptysis, root pressure, osmotic adjustment, growth
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Osmotic and elastic adjustment
• Osmotic and elastic adjustment (growth, drought, salinity, low temperature, etc.), induction by decrease in soil water potential, air humidity, etc.
• Osmotic adjustment – ion uptake, production and accumulation of osmotically active substances such as sugars (glucose, trehalose, saccharose), sugar alcohols (mannitol, sorbitol, glycerol), polyamines, amino acids (proline), betaines (glycinebetain)
• Membrane protection, source of C or N, defence against reactive oxygen species (ROS)
• Dehydrines – ripenning of seeds or pollen grains, in plant vegetative parts during stresses, induced also by abscisic acid (ABA)
• Elastic adjustment – expansin, endoglucanase, transglycosylase, peroxidase
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Changes in water potential and its components during water stress
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Water and growth
• Elongation:
• dV/Vdt m(p - Y)
• m - cell wall extensibility, p - pressure potential, Y - threshold pressure potential
• dV/Vdt Lp(wo - w)
• Lp - hydraulic conductance, wo - water potential of water source, w - water potential of
elongating cell
• Lockart equation:
• dV/Vdt = mLp/(m + Lp) (w + p - Y)
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Model of cell wall and possible changes of its extensibility
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Aktivity of xyloglucan endotransglycosylase
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Comparison of shoot and root growth rate as affected by water potential of substrate
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Water stress and growth
• Elongation rate (a) and pressure potential (b) in different distance from root apex in two substrates of different water potential